1. Field of the Invention
The present invention relates to a rear wheel suspension controller for a vehicle, particularly to a rear wheel suspension controller which is effective against a single shock caused by a protrusion or a hollow of a road surface on which an automobile is running.
2. Prior Art
Conventionally, the spring constant, damping force, bush characteristic or stabilizer characteristic of each of various suspension components provided between a body of a vehicle and its wheels is altered under control depending on conditions of a road surface or running conditions of the vehicle in order to prevent the vehicle from being shocked or vibrated and keep the controllability and the stability of the vehicle good.
For example, there are inventions to alter the spring constant of air spring for an air suspension in accordance with the state of road surface such as published unexamined patent application No. sho 59-26638, those to alter the damping force of a shock absorber as well as the spring constant of an air spring such as published unexamined patent application No. sho 59-23712, those to alter the damping force of a shock absorber only such as published unexamined patent application No. sho 58-30542, those to alter the vehicle height such as published unexamined patent application Nos. sho 57-172808 and 59-23713, those to alter just the rigidity of a bush such as published unexamined utility model application No. sho 59-132408 and those to alter the rigidity of a stabilizer such as published unexamined utility model application Nos. sho 59-129613 and 59-135213.
The above-mentioned controllers detect the running state on the rough road by vehicle height sensor, alter a characteristic of each suspension, maintain the controllability and the stability during rough road running and prevent dive, squat, rolling, etc. in case of predicting the sudden change of vehicle posture, e.g., dive, squat, rolling, etc. by brake lamp switch, throttle position sensor and steering sensor.
However, such conventional controllers judge the running state as bad only after severe changes are detected continuously by vehicle height sensors or vehicle height acceleration sensors in a predetermined interval and alter the suspension characteristics of all the wheels so as to achieve a predetermined effect. In such cases, they do not alter the characteristics of suspensions when passing over such kind of shock like a joint of road patches, a single protrusion or hollow of a road surface, because they resume running on a flat road after receiving a single shock.
Accordingly, in case of a single protrusion or hollow of a road surface, there is a difficulty in preventing an uncomfortable shock, vibration and noise for passengers and the controllability and the stability of the vehicle are deteriorated.
Further, even if they can alter the characteristic of the suspension after the judgment of a single protrusion or hollow, there is still such a problem that the controllability and stability are deteriorated when the change in the vehicle posture becomes severe during sudden turning, braking, accelerating, etc. of the running vehicle.